NAME apt_preferences - Preference control file for APT... How APT Interprets Priorities Priorities (P) assigned in the APT preferences file must be positive or negative integers. They are interpreted as follows (roughly speaking):

P >= 1000 causes a version to be installed even if this constitutes a downgrade of the package

990 <= P < 1000 causes a version to be installed even if it does not come from the target release, unless the installed version is more recent

500 <= P < 990 causes a version to be installed unless there is a version available belonging to the target release or the installed version is more recent

100 <= P < 500 causes a version to be installed unless there is a version available belonging to some other distribution or the installed version is more recent

0 < P < 100 causes a version to be installed only if there is no installed version of the package

P < 0 prevents the version from being installed

Also, the "origin" directive doesn't account for mirrors.

Another tip, to freeze a single package, don't pin it: `aptitude hold/unhold` it.